Electrodes are commonly, when in operation, immersed in an electrolyte in an electrolytic cell where chemical products are produced by way of oxidation and reduction reactions of reactants present in the electrolyte. The reduction reactions take place at the cathode where reduction products are obtained. The oxidation reactions take place at the anode where oxidation products are obtained.
Over time, the electrodes will become exhausted and deactivated due to various deactivation processes taking place while the electrolytic cells are in operation. In most electrolytic processes, the electric energy is the most expensive “raw material” in the electrolytic reactions.
In the chlorine and alkali metal hydroxide production, it has been found that the cathodes are liable to progressive deactivation over time. The cathodes are subjected to deposition and precipitation of materials present in the electrolyte and to other deteriorating processes deactivating the cathode. The decrease in activity leads to a higher power consumption due to an increased overvoltage.
It is thus a big concern in electrolysis processes to provide active cathodes throughout the whole electrolysis cycle.
Earlier attempts to solve this problem have involved transportation of the deactivated cathodes to the electrode manufacturer for reactivation. However, the transportation of cathodes is a very expensive and time-consuming alternative to carry out. Another approach of providing active cathodes has involved replacement of the exhausted cathodes with new ones.
U.S. Pat. No. 5,164,062 describes a method for preparing a new cathode comprising coating a cathode substrate of e.g. Ni with palladium and another electrocatalytic metal. The pH of the coating solution may be adjusted by an organic acid, e.g. acetic acid, oxalic acid and formic acid, or inorganic acids to maintain the pH below 2.8. However, the activation by this method is not always satisfactorily increased. Furthermore, a portion of the active coating solution is wasted in the method described above, because some of the acidic electrocatalytic coating solution is rinsed away from the cathode substrate in order to avoid corrosion of the cathode. The rinsing solution that has taken up remaining electrocatalytic material must then be decontaminated from substrate ions, e.g. nickel or other contaminating ions, which also are present on the cathode before the electrocatalytic material can be reused as coating material in an electrocatalytic solution again. Such decontamination procedure may involve several cleaning steps before the electrocatalytic material has been satisfactorily cleaned.
The present invention intends to solve the above problems.